If we were to create an equation for an individual's unique voice, it might looks something like this:

The shape of an individual's vocal tract is partly genetic, partly learned. Necks are long or short; pharynxes may be narrow or wide. While these attributes are genetically determined (except for configurations due to trauma or disease), individuals may also manipulate vocal tract shape. Highly trained singers have many tricks to change the contours of their vocal tracts to improve the sound coming out of their mouths. Lip rounding lengthens the vocal tract, for example.

Likewise, laryngeal anatomy is partially determined at birth: the length of one's vocal folds is determined by genes. However, the general hydration of one's vocal fold tissues or muscular agility of laryngeal muscles can be at least partly controlled by vocal health and training.

The learned component of the equation could also be called vocal habits. These would be items such as rhythm and rate of speech and vowel pronunciation. Rhythm, obviously, includes mannerisms such as periodic pauses to search for the right word, while rate refers to the speed of an individual's syllables and speech. (The average rate of speech for English speakers in the United States is about 150 words per minute, by the way.) A speaker's habits also influence how much air pressure is used to produce sound and how s/he uses laryngeal muscles to open and close the vocal folds.

So, should we be surprised that family members often sound alike? After all - for most of us - the home and the gene pool of our siblings, parents and children are shared.

How do we describe perceived vocal qualities?
The short answer: not very well. The average person easily recognizes familiar or famous voices, yet would have difficulty describing them in words. Language has not been as well developed for vocal characteristics as it has for appearance. People can be tall, bald or wrinkled, but how do we describe how they sound?

Despite their training, vocologists and voice researchers also disagree about exact descriptions of vocal qualities. Below is a table of terms suggested by Dr. Ingo Titze at the 8th Vocal Fold Physiology Conference in April 1994. The list is likely incomplete and does not necessarily reflect a consensus of the conference or the field of vocology as a whole. Ideally, a group of researchers and vocologists would organize a consensus conference in the future.

Voice Quality	Perception	Physiologic component
aphonic	no sound or a whisper	inability to set vocal folds into vibration, caused by lack of appropriate power (air pressure) or a muscular/tissue problem of the folds
biphonic	two independent pitches	two sources of sound (e.g., true folds and false folds, or two folds and whistle due to vortex in air)
bleat (see flutter)
breathy	sound of air is apparent	noise is caused by turbulence in or near glottis, caused by loose valving of laryngeal muscles (lateral cricoarytenoid, interarytenoid and posterior cricoarytenoid).
covered	muffled or 'darkened' sound	lips are rounded and protruded or larynx is lowered to lower all formants so a stronger fundamental is obtained
creaky	sounds like two hard surfaces rubbing against one another	a complex pattern of vibrations in the vocal folds creates a intricate formation of subharmonics and modulations
diplophonic	pitch supplemented with another pitch one octave lower, roughness usually apparent	a period doubling, or Fo/2 subharmonic
flutter	often called bleat because it sounds like a lamb's cry	amplitude changes or frequency modulations in the 8-12Hz range
glottalized	clicking noise heard during voicing	forceful adduction or abduction of the vocal folds during speech
hoarse (raspy)	harsh, grating sound	combination of irregularity in vocal fold vibration and glottal noise generation
honky	excessive nasality	excessive acoustic energy couples to the nasal tract
jitter	pitch sounds rough	fundamental frequency varies from cycle to cycle
nasal (see honky)
pressed	harsh, often loud (strident) quality	vocal processes of the arytenoid cartilages are squeezed together, constricting the glottis, and causing low airflow and medial compression of the vocal folds
pulsed (fry)	sounds similar to food cooking in a hot frying pan	sound gaps caused by intermittent energy packets below 70 Hz and formant energy dies out prior to re-excitation
resonant (ringing)	brightened or 'ringing' sound that carries well	epilaryngeal resonance is enhanced, producing a strong spectral peak at 2500-3500 Hz; in effect, formants F3, F4 and F5 are clustered
rough	uneven, bumpy sound appearing to be unsteady short-term, but persisting over the long-term	modes of vibration of the vocal folds are not synchronized
shimmer	crackly, buzzy	short-term (cycle-to-cycle) variation in a signal's amplitude
strained	effortfulness apparent in voice, hyperfunction of neck muscles, entire larynx may compress	excessive energy focused in laryngeal region
strohbass	popping sound; vocal fry during singing	sound gaps caused by intermittent energy packets below 70 Hz and formant energy dies out prior to re-excitation
tremerous	affected by trembling or tremors	modulation of 1-15 Hz in either amplitude or pitch due to a neurological or biomechanical cause
twangy	sharp, bright sound	often attributed to excessive nasality, but probably also has an epilaryngeal basis
ventricular	very rough (Louis Armstrong-type voice)	phonation using the false folds anterior rather than the vocal folds; unless intentional due to damage to the true folds, considered an abnormal muscle pattern dysphonia
wobble	wavering or irregular variation in sound	amplitude and/or frequency modulations in the 1-3 Hz range
yawny	quality is akin to sounds made during a yawn	larynx is lowered and pharynx is widened, as people do when yawning - hence the name

Vocal Awareness
As a fun exercise, listen carefully to the variety of voices you encounter in the next week or two. Try to characterize the voices according to the terminology in the above table. Are some qualities more pleasing to your ear than others? Do you notice similarities between biologically-related family members? Between spouses? Are there common qualities found in certain professions (for example, television or radio announcers)?

You may notice a recent preference for low-pitched and rough female voices. Perhaps the popularity of actresses such as Demi Moore and Kathleen Turner has brought this trend to the forefront. Of concern to vocologists is the temptation for females to try to mimic these celebrities by habitually speaking in pitches below a natural level. As has been discussed, a person's natural pitch is the healthiest for that particular individual.

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